Well, my Welsh isn’t all that great, but if I recall that means ‘The Dimpled Cheek’.
Explaining the pronunciation is a bit tricky. Particularly the first word. That double ‘l’ is an aspirated L. You say it by forming the mouth and tongue the way you would to say an L, but you just kind gently blow around the tongue without actually saying anything.
The closest most English speakers can get is to say it like an L with a th before it. The W is pronounced kind of like oo
So something like Toothl un ay boch (the ch in ‘boch’ is like in the Scottish ‘Loch’).
Gee..it sounds quite complicated! But thanks for your explanation, Tony. I don’t usually care to title for beginner’s music. To me pretty much of them are just nonsense and have a few (if not at all) relationship to the music. But this one really tickle my curiosity nerve